Tuesday May 20, 2008, 2:13 pm
NEW YORK (GenomeWeb News) – Using transgenic mice, Australian and American researchers have shown that they can “resurrect” a snippet of DNA from the genome of an extinct animal — the Tasmanian tiger — and test its biological function in a living animal.

In a paper to be published in tomorrow’s issue of the journal PLoS ONE, researchers from the University of Melbourne and the University of Texas plucked DNA from century-old Tasmanian tiger (Thylacinus cynocephalus) tissue samples and plopped it into mice. As predicted from sequence comparisons with living animals, the non-coding, regulatory DNA was expressed in the developing cartilage of mouse embryos.

“Up until now we have only been able to examine gene sequences from extinct animals,” lead author Andrew Pask, a zoologist at the University of Melbourne, said in a statement. “This research has developed to go one step further to examine extinct gene function in a whole organism.”

While this study provides insights into the role of that particular sequence, researchers say, the technique holds the potential for investigating broader questions, including the nature of gene evolution.

“Extinct genomes can now be accessed not just at the sequence level,” Richard Behringer, a molecular geneticist at the University of Texas MD Anderson Cancer Center and author on the paper, told GenomeWeb Daily News.

The Tasmanian tiger, or thylacine, was a carnivorous marsupial now believed to be extinct. Although it resembled domestic and wild dogs through convergent evolution, the thylacine was a marsupial that had a kangaroo-like pouch where its young developed.

The animal was hunted extensively in the early 1900’s and the last Tasmanian tiger died at Hobart Zoo in 1936. But the animal was not lost entirely. Tissue samples from adult and young thylacines that are some 100 years old have survived and are yielding genetic information.

Similar to other extinct animals, such as the mammoths and Neanderthals, researchers have been able to extract DNA from the Tasmanian tigers. But, for the moment at least, Behringer and his colleagues haven’t attempted to sequence the entire thylacine genome. Instead, they examined the function of a specific region in vivo in the transgenic mouse.

For this study, the researchers focused on a stretch of thylacine DNA that appeared to be similar to Col2a1, a non-protein coding enhancer found in living animals that typically ramps up collagen transcription.

First, they isolated genomic DNA from four samples obtained from Melbourne’s Museum Victoria: three young samples that had been preserved in alcohol and a patch of dried pelt. Then they amplified DNA from a region containing sequence similar to Col2a1 using primers designed to recognize conserved mammalian sequences.

The product, a 264-basepair insert, was distinct from other sequences in the BLAST database, though it appeared to be most closely related to the Col2a1 enhancer from a fellow marsupial, the tammar wallaby.

By fusing the thylacine sequence to a reporter gene, the team was able to watch the expression pattern of the potential Col2a1 sequence after injecting it into mouse zygotes. As expected, the thylacine DNA was expressed in the same place as mouse Col2a1 — in developing limb cartilage.

At this point the research has provided proof-of-principle evidence that Tasmanian tiger DNA can be transplanted into other animals. In the future, Behringer said, the team may transplant other thylacine sequences, such as protein-coding and/or species-specific sequences, into living animals as well. So far, though, attempts to express thylacine protein-coding regions in mice have been unsuccessful.